1. Field of the Invention
The present invention relates to a device for judging acceleration of an automotive engine, and to a control system using the acceleration judging device for controlling a fluid coupling of an automotive automatic transmission.
2. Description of Related Art
To determine the acceleration of an automotive engine, it is well known to use a specific reference value for judging when acceleration of the engine occurs. When a level of engine load increases beyond the specific value, the engine is judged to be in acceleration. Upon the detection of acceleration of the engine, a lockup clutch is released to unlock a fluid coupling of an automatic transmission, such as a torque converter, so that the torque converter allows slippage and permits the engine torque to multiply with high performance, thereby allowing the engine to accelerate quickly. An acceleration judging device, or system, of this kind is known from, for instance, Japanese patent application No. 56-134508, entitled "Control System For Automatic transmission with Direct Coupling Clutch," filed on Aug. 27, 1981 and published as Japanese Unexamined Patent Publication No. 58-37368 on Mar. 4, 1983.
When an engine operated element, such as an air conditioner, is in use, the engine is subjected to higher, or heavier, loads. For this reason, it is necessary for a driver of the vehicle to depress, or push down, an accelerator pedal more deeply when the air conditioner is in use than when it is not in use in order to speed the vehicle up at the same acceleration rate, even if the vehicle is running at the same speed. However, if the value for the judgement of acceleration is set to a higher value, suitable for engine operating conditions during times when the air conditioner is in use, the value becomes too high to properly judge the acceleration of engine when the air conditioner is not in use. On the other hand, if the acceleration value judgement value is set to a lower value, suitable for engine operating conditions during times when the air conditioner is not in use, the value becomes too low. If the acceleration judgment value is too low, frequently, the control system will misjudge the acceleration of the engine, and detect an acceleration, even though the engine is not actually in acceleration, while the air conditioner is in use. Accordingly, it is likely that the lockup torque converter, which is adapted to be unlocked during acceleration, will multiply engine torque uncertainly sometimes during an acceleration of the engine. This results in having the engine undesirably accelerate at different rates under various operating conditions. This is true, for instance, for an engine which is subjected to loads from a power steering system or to fluctuations, or changes, in engine load caused from, for instance, a sloped road.